KR20070085963A - Conductive silver dispersions and uses thereof - Google Patents

Abstract

Silver particles having controlled and predetermined properties of size, morphology and size distribution for use in manufacturing of conductive inks, conductive fillers and/or conductive coatings are provided by forming a dispersion of silver halide particles in a carrier medium such as gelatin and treating the dispersion such that the silver halide particles are converted into the desired silver particles.

Description

Conductive Silver Dispersions and Their Uses {CONDUCTIVE SILVER DISPERSIONS AND USES THEREOF}

The present invention relates to silver dispersions and conductive materials, in particular conductive inks, conductive tracks, and their use as electronic circuit boards and devices using these conductive inks and conductive tracks, and methods of making them. The present invention relates in particular to a process for the preparation of these silver dispersions in which they can advantageously control the conductivity, particle size, size distribution, morphology and other properties of the silver dispersion.

In the imaging, lighting, display and electronics industries, electronic products are expected to be increasingly durable, thinner, lighter and cheaper to meet consumer demand and also to drive industrial competition. In a growing market where consumers demand more from portable electronic devices and displays, such as mobile phones, laptop computers, and the like, flexible displays and electronic devices can remove the rigid constraints of traditional flat panel displays and electronic products. The purpose in displays and electronic devices is to manufacture thin, lightweight, flexible devices and displays with power requirements attainable at minimal cost.

Due to the recent developments in the printing industry, functional inks, in particular in electronics in the form of backplane structures for RFID tags, printed circuits, photovoltaics and display devices, and also in conductive inks that can be used in the manufacture of electronics. Attention has been focused. Using the printing method to apply conductive ink to a substrate, there is a greater possibility of producing large quantities and low cost electronic components using a flexible substrate on which conductive tracks can be printed.

Dispersions of conductive particles that can be used in inks are particularly highly inclusive of copper, silver coated copper, silver, platinum and gold, as necessary to achieve the required conductivity using relatively small amounts of conductive material compared to traditional electronics methods. It may comprise a mixture of conductive particles or flakes. In particular, silver particles or flakes are used in conductive inks, conductive adhesives and RF / EM shielding additives for plastics and coatable conductors.

Several methods are known for using silver dispersions in conductive inks and coatable conductors that must be applied to flexible or rigid substrates.

US-B-6379745 is intended to be applied to a temperature-sensitive substrate and cured to produce high electrical conductivity results at temperatures that the substrate (rigid glass-reinforced epoxy laminates and polyimide films for flexible circuits) can withstand. Disclosed are printable compositions. The composition can be applied by any convenient printing technique, including screen printing, stencils, gravure printing, impression printing, offset printing, and ink-jet printing. The described composition comprises a metal powder mixture and a reactive organic medium. The metal powder mixture is a mixture of two or more types of metal powders: colloidal or semi-colloidal metal powder having a major diameter of about 5 μm and a thickness to diameter ratio of 10 or more, and an average diameter of less than about 100 nm that is not highly aggregated. . The metal is typically copper or silver. The reactive organic medium may consist of any metal-organic compound, such as a metal soap, which can be readily decomposed into the corresponding metal.

US-B-6797772 relates to a storage-stable silver-filled organosiloxane composition that produces a cured electrically conductive elastomer that retains electrical properties for a long time. This composition treats finely divided silver particles with an organosilicon compound before combining the particles with the other components of the curable organosiloxane composition, thereby reducing the poor curability of the electrically conductive silicone rubber composition and the reduction between the cured silicone elastomer and the silver particles. It overcomes the problems of the prior art such as the adhesion and the affinity which are made. The resulting conductive silicone rubber composition comprises a polyorganosiloxane containing at least two alkenyl radicals per molecule, organohydrogensiloxane, finely divided silver particles and at least two silicon-bonded hydrogens in each molecule, and curing of the composition. Platinum-containing hydrogenated siliconization reaction catalyst to promote the reaction.

US-B-6322620 describes screen printable thermosetting conductive inks for use in through hole interconnects or similar electronic applications. The thermosetting conductive inks described comprise a thermosetting resin system having a mixture of about 50 to 90 percent by weight of an epoxy resin, a crosslinker and a catalyst, an organic solvent, and an electrically conductive material (especially silver flakes) such as silver, copper, silver-coated copper. Include. Thermosetting conductive inks have been reported to have high electrical conductivity and are stable at high temperatures for a short time after curing and have good adhesive strength and good solvent resistance.

US-B-6558746 relates, in particular, to coating compositions for preparing electrically conductive coatings for electromagnetic shielding (EMI screening) of electronic devices such as personal computers and mobile phones, which compositions may be dispersed in one or more conductive pigments and water. Organic binders and aqueous solvents, which are copolymers based on (meth) acrylates and silylated unsaturated monomers. Conductive coatings with excellent adhesive strength, mechanical resistance and solvent resistance can be obtained. Preferred conductive pigments are silver flakes and copper flakes.

WO-A-03 / 068874 discloses a conductive ink for gravure or flexo printing an RFID tag on a package or the like, which conductive ink may be a carboxylic acid or anhydride-functional aromatic vinyl polymer and an electric which may be particulate or flake material. Conductive materials, especially conductive flake materials having an aspect ratio of at least 5: 1. The conductive particulate material may be a conductive metal oxide, such as tin antimony oxide or indium tin oxide, or may be a metal such as silver, aluminum or copper. The ink is preferably metal flakes such as mica, typically coated with graphite, carbon fiber, antimony or indium oxide, silver, copper or aluminum flakes having an aspect ratio of at least 5: 1, preferably from 10: 1 to 50: 1. Also included are conductive flake materials.

US-B-6517931 describes a method of using conductive silver inks to fabricate multilayer ceramic capacitor (MLC) devices. The silver inks described typically comprise high purity silver powder having an average particle size of at least 1 μm or less; Inhibitors such as substances based on barium titanate; And a vehicle comprising a mixture of a resin (eg ethyl cellulose) and a solvent (eg a toluene / ethanol mixture). In accordance with US-B-6517931, the ink is screen printed in a desired pattern on a dielectric green tape that is made up of stacked, stacked registry under pressure and then fired to produce an MLC device.

WO-A-97 / 48257 describes lithography of electrically conductive inks onto a substrate in the manufacture of various electrical components such as resistors, capacitors, and circuit boards having less complex circuits, in particular as substitutes for conventional copper clad circuit boards. . Preferred electrically conductive inks according to WO-A-97 / 48257 comprise about 1 μm of metallic silver (eg, about 80% w / w) suspended in organic resins such as alkyd resins. Lithographic printing in layers of about 5 μm allows the ink to be applied to substrates such as glossy art paper, bond paper or semi-synthetic or synthetic paper. The conductive ink described is used to obtain appropriate mechanical and electrical properties. It is implied that the ink must exhibit high electrical conductivity in order to accommodate this small ink laydown.

A particular problem with the silver dispersions of the prior art involves the amount of silver that must be applied to the substrate to achieve the required conductivity as much as the overall cost of the substrate and the reduction of other components in the field of flexible electronics. Another problem is that it is difficult to achieve high resolution conductive tracks, especially by printing conductive inks, which limits the use of conductive inks in the manufacture of electronic devices and the like of less complex circuits.

Problems to be Solved by the Invention

It is desirable to provide a dispersion of silver particles having a particle size, shape, and particle distribution that is highly controlled to meet the specific conditions of the intended use in terms of conductivity, resolution, consistency and cost.

It is desirable to provide a method of producing a dispersion of silver particles or silver powder that precisely adjusts the size, shape and size distribution of the particles to meet these conditions.

It is also desirable to provide conductive inks comprising silver particles that have improved conductivity and can provide improved resolution at relatively low silver laydowns, and therefore at reduced cost.

Summary of the Invention

According to a first aspect of the present invention, there is provided a method of preparing a conductive ink, conductive filler and / or conductive coating comprising silver particles for imparting conductivity alone or in combination with other conductive materials, the method comprising a carrier medium Providing a dispersion of silver halide particles in water; Treating the dispersion of silver halide particles such that the silver halide particles are converted to silver particles to produce a dispersion of silver particles in a carrier medium; And further processing the dispersion of silver particles in the carrier medium to produce a conductive ink, a conductive filler and / or a conductive coating.

In a second aspect of the present invention there is provided a conductive ink, conductive filler or conductive coating obtainable by the method.

In a third aspect of the invention, there is provided a conductive ink for ink-jet printing comprising a dispersion of silver particles having silver particles in the form of cubic or tabular shapes, wherein the dispersion has a coefficient of variation of 0.5 or less. Has a size distribution.

In a fourth aspect of the present invention, there is provided a conductive ink for lithography comprising a dispersion of silver particles having silver particles having a maximum dimension of 10 μm or less and a flat plate shape of aspect ratio of 5: 1 or more.

In a fifth aspect of the present invention, there is provided a conductive filler comprising a dispersion of silver particles having a maximum dimension of 10 μm or less and a plate shape of at least an aspect ratio of 5: 1.

In a sixth aspect of the present invention, there is provided a conductive coating comprising a dispersion of silver particles having a maximum dimension of 10 μm or less and a plate shape of at least an aspect ratio of 5: 1.

In a seventh aspect of the invention, there is provided a dispersion of silver halide particles in a carrier medium, the process comprising treating the dispersion of silver halide particles such that the silver halide particles are converted to silver particles to produce a dispersion of silver particles in the carrier medium. There is provided a method of producing a silver dispersion for use as or in the manufacture of conductive inks, conductive fillers and / or conductive coatings, the method characterized by a dispersion of silver particles having one or more of the following features: :

A) Coated conductivity expressed as resistivity of 1000 Ω / square or less;

B) at least 50% of plate-like silver particles having an aspect ratio of at least 3: 1; And

C) size distribution of particles having a coefficient of variation of 0.4 or less.

In an eighth aspect of the invention there is provided a dispersion of silver particles for use as or in the manufacture of conductive inks, conductive fillers and / or conductive coatings, wherein the dispersion of silver particles is indicated by a resistivity of 1000 Ω / square or less. Silver particles dispersed in a carrier medium at a concentration capable of imparting conductivity to the ink, filler and / or coating prepared therefrom, the silver particles having a flat form and having an aspect ratio of at least 3: 1 and / or having a silver dispersion Silver has a size distribution of silver particles having a coefficient of variation of 0.5 or less.

In a ninth aspect of the present invention, there is provided a method of manufacturing an electronic circuit, comprising applying a dispersion of silver particles as defined above to a substrate in a desired pattern of conductive tracks.

In a tenth aspect of the invention, the silver halide particles are treated with a dispersion of silver halide particles such that the silver halide particles are converted to silver particles to form a dispersion of silver particles, from which a conductive ink, conductive filler or conductive coating is produced, thereby forming a conductive ink, conductive filler and / or the like. Or the use of silver halide particles in the manufacture of conductive coatings.

In an eleventh aspect of the present invention, by controlling the dispersion of silver halide particles such that the dispersion of silver halide particles is converted into a dispersion of silver particles, for controlling the individual size, size distribution and / or shape of the silver particles in the dispersion of silver particles, The use of factors to control the size, size distribution and / or morphology of silver halide particles in preparing a dispersion of silver halide particles is provided.

In a twelfth aspect of the present invention, the individual physical and chemical development of the fogging silver halides for controlling the morphology of the silver particles produced by treating the silver halide particles such that the silver halide particles undergo a fogging step and a developing step The use of factors to control is provided.

Advantageous Effects of the Invention

According to the process for the preparation of dispersions of silver and conductive materials according to the invention, silver dispersions can be specially formulated according to the intended use, physical conditions and cost-sensitiveness. This method can be used to strictly control the particle size, size distribution, dimensions and shape according to the conditions required to maximize the conductivity of the conductive ink, for example at a minimum laydown of silver.

1 shows an SEM image at 5000 times magnification of 100% silver chloride cube particles.

FIG. 2 shows an SEM image at 5000 times magnification of the cube silver particles prepared from the silver chloride particles of FIG. 1.

FIG. 3 shows SEM images at 10,000 times magnification of 100% silver chloride flat [100] particles.

FIG. 4 shows an SEM image at 10,000 times magnification of flat silver particles prepared from the silver chloride flat [100] particles of FIG.

FIG. 5 shows SEM images at 10,000 × magnification of 100% silver chloride flat [111] particles. FIG.

FIG. 6 shows an SEM image at 10,000 times magnification of planar silver particles prepared from the planar [111] silver chloride particles of FIG.

FIG. 7 shows an SEM image at 5000 times magnification of silver particles prepared from the silver chloride flat plate [100] particles of FIG. 5 fogging with SnCl ₂ .

The process of the present invention includes preparing silver dispersions in a carrier medium, which dispersions can typically be used in the manufacture of various components, in particular for use in the electronic device, display and printing industries. For example, silver dispersions prepared according to the method of the present invention produce conductive inks for use in printing conductive tracks on circuit board substrates or other electronic devices, such as in various electronic devices such as mobile phones and laptop computers. As conductive fillers for use in shielding, it is also possible to use silver dispersions as coatable conductors which can be coated onto supports to produce conductive layers or conductive tracks, for example in circuit boards or photovoltaic backplates.

According to the method of the present invention, a dispersion of silver halide particles is provided to a carrier medium, and the silver halide particles are processed to be converted into silver particles to form a dispersion of silver particles in the carrier medium. The dispersion of silver particles may then be applied in one or more further steps, as described below, to use the silver dispersion as a conductive ink, conductive filler or to prepare a conductive coating.

The carrier medium used may be any suitable carrier in which the silver halide particles can form a dispersion and the silver halide can be converted to silver particles. Preferably, the carrier medium is suitable for precipitating silver halide particles from silver ions and halide ions. Typically, the carrier medium used is any carrier medium used in the field of photography, in which a silver halide emulsion for photography is prepared. Suitable carrier media include, for example, naturally occurring hydrophilic colloids and gums (e.g., gelatin (e.g., alkali-treated gelatin such as bovine or hydrogelatin, or acid treated gelatin such as porcine shell gelatin), albumin, guar, xanthan, Arabia, chitosan and derivatives thereof, functionalized proteins, functionalized gums and starches, cellulose ethers, esters and derivatives thereof (e.g. hydroxyethyl cellulose, hydroxypropyl cellulose and carboxymethyl cellulose), sulfonated Polyesters, polyvinyl oxazolines and polyvinyl methyloxazolines, polyoxides, polyethers, poly (ethylene imine), poly (acrylic acid), poly (methacrylic acid), acrylamide polymers and polyvinyl pyrrolidone n-vinyl amide, polyethylene oxide, polyvinyl alcohol, poly (vinyl lactam), polyvinyl acetal, alkyl and sulfoalkyl acrylates And polymers of methacrylates (eg, substituted poly (hydroxyalkyl (meth) acrylates) and unsubstituted poly (hydroxyalkyl (meth) acrylates)), hydrolyzed polyvinyl acetates, polyamides, meta Krillamide copolymers [eg, substituted and unsubstituted poly (hydroxyalkyl (meth) acrylamides)] and poly (meth) acrylates and optionally poly (meth) acrylamides with poly (alkene oxide) substituents, Latex copolymers, polyethylene glycols, polyglycidol and / or combinations of any of the above. Suitable carrier media are preferably poly (vinyl alcohol), partially hydrolyzed poly (vinyl acetate-co-vinyl alcohol), hydroxyethyl cellulose, poly (acrylic acid), poly (1-vinylpyrrolidone), poly ( Water soluble polymers or copolymers, including but not limited to sodium styrene sulfonate), poly (2-acrylamido-2-methane sulfonic acid) and polyacrylamide, or copolymers of these polymers with hydrophobic monomers , More preferably gelatin or modified gelatin (eg, acetylated gelatin, phthalated gelatin, oxidized gelatin or diamine derived gelatin). The gelatin may be a base-processed gelatin, such as lime-processed gelatin, or may be an acid-processed gelatin, such as acid-processed collagen gelatin. More preferably, the carrier medium is gelatin.

The silver halide can be any silver halide or combination of silver halides. The silver halide dispersion may comprise one or more of silver chloride, silver bromide and silver iodide, but preferably it comprises silver chloride alone or in combination with silver bromide and / or silver iodide. More preferably, the silver halide dispersion comprises at least 50%, even more preferably at least 80%, more preferably at least 90% (eg 95 to 98%), even more preferably at least 99.5% of silver chloride, most preferred Preferably it consists essentially of silver chloride and even more preferably comprises 100% silver chloride.

According to the invention, the silver halide dispersion provided in the carrier medium, which is preferably gelatin, is treated to convert the silver halide particles into silver particles. This conversion can be accomplished by any suitable method of converting silver halides to silver, but preferably the majority of the particles are converted in a controlled manner such that the majority of the particles are relatively short in time, but with some control over the size and shape of the silver particles. It is done by a very efficient way that can be done.

Typically, the conversion of silver halide particles to silver particles involves a two step process. First, silver halide particles are "fogged" to produce silver halide particles in which some of the silver halide molecules are reduced to silver atoms. Secondly, the developer particles are "developed" using the developer composition to convert the silver halide particles into silver particles.

The fogging step of the silver halide particles can be carried out in any number of suitable ways. For example, by treating silver halide particles with one or more reducing agents, exposing the silver halide particles to radiation they are sensitive to, adjusting the pH of the silver halide dispersion, and / or incorporating a source of silver ions or silver ions into the silver halide dispersion. By doing so, the silver halide particles can be fogged.

Suitable reducing agents for fogging silver halide particles include, for example, tin chloride and DMAB (dimethyl borane).

When fogging silver halide particles by exposure to a source, it is preferable to use a light source of a wavelength at which the particles are sensitive. The use of spectrally sensitized silver halide particles makes this fogging method much more efficient. Any suitable spectroscopic sensitization method can be used as is common for photographic silver halide emulsions. Such suitable spectroscopic methods are described, for example, in Research Disclosure, Item 37038, February 1995, Sections I to V.

Silver ions can be used to fogging silver halide emulsions, for example, by adding excess silver ions during precipitation of silver halide particles, or by incorporating a suitable silver ion source in the silver halide dispersion.

When fogging silver halide particles by raising the pH of the dispersion of silver halide particles, it is preferable to raise the pH to 9 or more, typically 9 to 14, preferably about 12. Optionally, the pH can be maintained at this level for a short time sufficient for at least some fogging to occur, or it can be maintained for a more substantial period of time to ensure widespread fogging of the particles.

Typically, the pH is increased by adding a base, such as sodium hydroxide solution, to the silver halide dispersion.

Developing the fogging silver halide particles may include any suitable development method. The developer composition includes a component that can cause deformation of the silver halide particles that are fogging into the silver particles. Typically, the developing step includes treating the fogging silver halide particles with the developer composition or activating the latent developer composition. Such suitable developer compositions include developers known to be used in photographic (color or black and white) development processes, and preferably include one or more of, for example, ascorbic acid, sodium erytolate, hydroquinone and derivatives thereof. . Preferred developer compositions include ascorbic acid, sugar form derivatives of ascorbic acid, stereoisomers, diastereoisomers, precursors of these acids and salts, preferably ascorbic acid itself.

The latent developer composition (or developer incorporated) is a developer composition capable of transforming the silver halide particles that are fogging after activation into silver particles. These suitable latent developer compositions include, for example, ascorbic acid maintained in solution at a pH of less than 7. By raising the pH of the composition, such latent developer compositions can be activated.

Once development is initiated, it is common for the pH of the dispersion of particles to temporarily decrease (eg, below pH 9) and then return to a higher pH. Optionally, for example, in order to maintain a high development rate (especially when using a latent developer composition which is activated at a certain minimum pH), in particular during the first few minutes of development the dispersion is treated with a base such as sodium hydroxide solution, It is possible to counteract this decrease in pH, limit the decrease in pH of the dispersion and maintain or raise the pH of the dispersion.

In one preferred embodiment, the fogging and developing step of treating the silver halide particles is a single step comprising increasing the pH of the silver halide dispersion comprising a latent developer composition that can be activated by actually increasing the pH. Raising the pH of the silver halide dispersion has the effect of fogging the silver halide particles and activating the developer composition.

Optionally, the developer composition further comprises a co-developer or development accelerator. Such suitable co-developers are disclosed in EP-A-0758646, EP-A-0528480 and US-A-4753869 and include, for example, aminophenols such as methyl-p-aminophenol sulfate; And 1-phenyl-3-pyrazolidone, 1-phenyl-4-methyl-3-pyrazolidone, 1-phenyl-4,4'-dimethyl-3-pyrazolidone and 1-phenyl-4-methyl Phenyl-3-pyrazolidone or phenidone, such as -4'-hydroxymethyl-3-pyrazolidone (HMMP). Preferred co-developers are HMMP. Phenyl-3-pyrazolidone or phenidone co-developers, in particular HMMP, are especially used with developers such as ascorbic acid, sugar form derivatives of ascorbic acid, stereoisomers, diastereoisomers, precursors of these acids and salts. Co-developers may be particularly useful where it is necessary to physically develop the silver halide particles to produce pseudomorphic silver particles. Analogous form refers to silver particles which retain most of the form of the silver halide particles formed thereof.

The conversion or development of silver halide particles to silver particles can be characterized by physical and / or chemical phenomena. Phenomena, which are mostly physical phenomena, tend to produce silver-like particles, whereas chemical phenomena change the shape of silver particles (compared to silver halide particles).

Optionally, the developer composition may also include a fixing agent to further control the size and shape of the silver particles produced by this method by inspiring the physical development of the silver halide particles. The use of fixatives in developer compositions has been found to be particularly effective in controlling the form of silver particles produced when fogging silver halide particles by raising the pH of the silver halide particle dispersion. Any suitable fixing agent can be used, but preferably sodium sulfite is used.

When the fixer is incorporated into the developer composition and then added to the fogging silver halide dispersion, or when the developer composition is latent (or incorporated) in the silver halide dispersion, the developer composition is activated (eg, contains ascorbic acid). When the pH of the silver halide dispersion is raised), a fixing agent may be added to the silver halide dispersion.

The characteristics of the silver particles in the dispersion of silver particles prepared according to the present invention can be preferably adjusted by selecting an appropriate measure at each step involved in preparing the dispersion of silver particles. For example, the shape of the resulting silver particles, the size and size distribution of the particles formed in the dispersion and the conductivity of the dispersion can be controlled.

By controlling the shape of the silver halide particles provided and / or by controlling the conversion of the silver halide particles to silver particles, the size, shape and size distribution can be controlled.

In order to produce a large plate-like particle such as flat silver particles (or silver platelets) by adjusting the shape of the silver particles in the prepared dispersion, a silver halide dispersion having a desired shape, that is, a large plate- or plate-like structure Silver halide particles may be provided. As discussed above, the conversion process can be selected to change or maintain the size and shape of the particles.

As mentioned above, another aspect of controlling the shape of the silver particles produced is to control the conversion of silver halide particles to silver particles. Preferably, for example, in order to maintain most of the shape of the silver halide particles in the silver particles (to prepare the similar form silver particles), to minimize the change in the shape of the silver halide particles during development for producing the silver particles, the silver halide particles (the By controlling the size and shape of the silver particles).

Thus, rather than chemical phenomena, conditions favoring the physical phenomena that produce silver particles, which are mostly similar in form to corresponding silver halide particles, are preferred.

In particular, it is possible to use silver chloride high halide particles, preferably 100% silver chloride particles, which are more easily physically developed, especially when ascorbic acid or derivatives are developer and particularly when the silver halide particles are fogging using pH, such as HMMP. It is preferred to use co-developers and to encourage physical phenomena using fixatives such as sodium sulfite. Conditions favorable to these physical phenomena—silver halide particles, co-developers, fixers—with a high chloride content can be used individually or in combination, most preferably all of these conditions are adopted.

Thus, using the method of the present invention, it is possible to adjust the desired size and shape of the silver particles according to the use in which they are used. The described parameters can be varied to produce silver particles, for example in the form of T-grains, cubes, filaments or rods. T-grains, cubes or rods are preferably produced by controlling the production of silver halide particles to produce silver halide particles having the desired shape, followed by the conversion of silver halide particles to minimize morphological changes. By adjusting the production of silver halide particles to encourage crystal growth in the desired dimensions, and by using conditions that encourage chemical phenomena, for example, the silver particles of the halide particles can be made to further extend the dimensions of the particles in the form of filaments and / or rods. By controlling the conversion of filaments and more or less rods can be produced.

The factors (and the following factors) are individually or preferably to control the individual physical and chemical developability and / or to control the size, size distribution and / or shape of the silver particles when producing silver particles from silver halide particles. Useful in combination.

Preferably, in the process according to the invention, providing a dispersion of silver halide particles in the carrier medium is preferably silver halide particles in the carrier medium by precipitating silver halide particles (or grains) from silver ions (eg from silver nitrate) and halide ions. Producing a dispersion of particles.

In the following discussion of materials suitable for use in the silver halide dispersions described herein, Research Disclosure , Sep. 1994, Item 36544, Kennets Mason Publications, Limited (Hampshire Pi010 7 Dec. Emsworth 12 A. North Street, UK) Dudley Annex) (hereinafter referred to as "Research Disclosure"). The contents of the Research Disclosure, including patents and publications referenced therein, are incorporated herein by reference, and the following sections refer to the sections of the Research Disclosure.

Suitable silver halide dispersions (called silver halide emulsions in the photographic field) and their preparation methods are described in sections I to V. Other additives that may be useful in the present invention (eg, chemical sensitizers and spectroscopic sensitizers, antifogging agents and coating aids, etc.) are also described in the Research Disclosure.

As described above, any combination of silver halides such as silver chloride, silver chlorobromide, silver chlorobromoiodide, silver bromide, silver bromoiodide or silver chloroiodide can be used. If the composition comprises mixed halides, minor components can be added during crystal formation or during an optional sensitization step after crystal formation. The shape of the silver halide particles or grains may be cubic, quasi-cubic, octahedral, tetrahedral or flat, required or required for the particular application in which the resulting silver particles are used. The particles may be precipitated to produce the dispersions required in any suitable environment (eg, ripening environment, reducing environment or oxidizing environment).

Specific references relating to the preparation of dispersions or emulsions of different halide ratios and forms are described in EP-A-1321812, US-A-3618622, US-A-4269927, US-A-4414306, which are incorporated herein by reference. , US-A-4400463, US-A-4713323, US-A-4804621, US-A-4738398, US-A-4952491, US-A-4493508, US-A-4820624, US-A-5264337, US-A-5275930, US-A-5320938, US-A-5550013, EP-A-0718679, US-A-5726005 and US-A-5736310.

Precipitation of the silver halide particles into a dispersion (or emulsion) is carried out in an aqueous dispersion medium comprising a peptizer, typically at least during particle or grain growth, in the presence of silver ions, halide ions. Particle or grain structures and properties can be selected by controlling the precipitation temperature, pH and relative amounts of silver and halide ions in the dispersion medium. In preparing photographic silver halide emulsions, precipitation is usually carried out on the halide side of the equivalence point (the point where the silver ion activity and the halide ion activity are the same) to avoid fog. In the present invention, precipitation can be carried out at the equivalence point or at the halide or silver side. Manipulation of these basic parameters is exemplified by the cited literature, which includes photographic emulsion settling content, US-A-4497895, US-A-4728603, US-A-4755456, US-A-4847190, Further illustrated are US-A-5017468, US-A-5166045, EP-A-0328042 and EP-A-0531799. In one embodiment of the invention, precipitation can be carried out on the silver side of the equivalence point to produce fog in the resulting silver halide particles.

US-A-5061614, US-A-5079138, EP-A-0434012, US-A-5185241, EP-A-0369491, EP-A-0371338, EP-A-0435270, EP As illustrated in -A-0435355 and EP-A-0438791, it is possible to incorporate reducing agents into the dispersion medium during precipitation, and these reducing agents can be used to increase the susceptibility of silver halide particles. Conversely, as exemplified in JP 56-167393, JP 59-195232, EP-A-0144990 and EP-A-0166347, it is possible to incorporate oxidants during precipitation and to pre-treat them in the dispersion medium (gelatin). It can be used as a solvent or added to the dispersion after the preparation of silver halide particles in order to reduce the tendency of silver halide to be fogged or to minimize residual maturing. As illustrated in US-A-3206313, US-A-3327322, US-A-3761276, US-A-4035185, and US-A-4504570, chemically sensitized core grains precipitate the shell. Can serve as a host for

Fogging inhibitors, chemical sensitizers and spectroscopy that are adsorbed on silver halide particles or grain surfaces and thus can be used to control or inhibit particle growth from one or more surfaces of silver halide particles during or after precipitation or to control the effects of phenomena on morphology. Additives such as sensitizers may be added to the silver halide dispersion during or after precipitation.

Precipitation in the presence of spectrosensitizing dyes is described in US-A-4183756, US-A-4225666, US-A-4683193, US-A-4828972, US-A-4912017, US-A-4983508, It is exemplified in US-A-4996140, US-A-5077190, US-A-5141845, US-A-5153116, EP-A-0287100 and EP-A-0301508. Non-dye additives are exemplified in US-A-4705747, US-A-4868102, US-A-5015563, US-A-5045444, US-A-5070008 and EP-A-0392092. Water soluble disulfides are exemplified in US-A-5418127.

Chemical sensitizers effective for this purpose include sulfur sensitizers, sulfur and gold sensitizers or gold sensitizers. Typical gold sensitizers are chloroorate, gold dithiosulphate, aqueous colloidal gold sulfide or orus bis (1,4,5-trimethyl-1,2,4-triazol-3-thiolate) tetrafluoro Roborate (eg, US Pat. No. 5,049,485). Sulfur sensitizers are thiosulfate, thiocyanate, N, N'-carbothioyl-bis (N-methylglycine) or 1,3-dicarboxymethyl-1,3-dimethyl-2-thiourea sodium salt It may include.

As mentioned above, a flat silver halide particle dispersion may be used in the present invention to produce a flat silver silver dispersion. Specifically contemplated planar particle dispersions are planar particles having at least 50% of the total projected area of the particles having a thickness of less than 0.5 μm, preferably of 0.3 μm and an average flatness T of at least 25 (preferably at least 100). This is due to the grain. Here, the term "flatness" is used for the purpose recognized in the art (silver halide emulsion for photography) as in the following equation:

T = ECD / t ²

In the above formula, ECD is the average equivalent circular diameter (μm) of plate grain,

t is the average thickness (micrometer) of planar grains.

The useful average ECD of the photographic emulsion can be about 10 μm and is low enough to be usefully achieved. The flat grain thickness may be about 0.02 μm or less. However, smaller platelet grain thicknesses are considered. For example, US Pat. No. 4,672,027 to Doubendiek et al. Reports a flat grain silver bromoiodide emulsion having a grain thickness of 0.017 μm and containing 3 mol% iodide. Emulsions with a high chloride content of ultra thin platelet grains are disclosed in US Pat. No. 5,217,858 to Masskasky.

As indicated above, planar particles below the prescribed thickness occupy at least 50% of the total particle projection area of the dispersion. In order to maximize the benefit of high flatness, it is generally desirable for flat grains that meet the stated thickness criteria to occupy the conveniently attainable highest percentage of the total grain projection area of the dispersion. For example, in a preferred dispersion of planar particles, the planar particles that meet the aforementioned thickness criteria account for at least 70% of the total particle clear area. In a more preferred plate-like particle dispersion, the plate-like particles satisfying the thickness criteria occupy 90% or more of the total particle projection area.

Suitable flat grain emulsions can be selected from a variety of conventional teachings such as: Research Disclosure, Item 22534, January 1983 (Kenneth Mason Publications, Limited, Hampshire Pi010 7 Diddy Msworth); US-A-4439520, US-A-4414310, US-A-4433048, US-A-4643966, US-A-4647528, US-A-4665012, US-A-4672027, US -A-4678745, US-A-4693964, US-A-4713320, US-A-4722886, US-A-4755456, US-A-4775617, US-A-4797354, US- A-4801522, US-A-4806461, US-A-4835095, US-A-4853322, US-A-4914014, US-A-4962015, US-A-4985350, US-A -5061069 and US-A-5061616.

The silver halide dispersion is preferably surface-sensitive. That is, fog is generated mainly on the surface of the silver halide particles.

Silver halide particle dispersions and / or other components that may be included in the silver particle dispersions include nucleating agents, electron transfer agents, development accelerators, and surfactants.

To control the development of silver halide particles into silver particles in terms of development speed (a form of control) and / or morphological change during development (e.g., development occurs preferentially at a location on or within the silver halide particles and Elsewhere in the present invention), nucleating agents, electron transfer agents and development accelerators may be useful.

Suitable nucleating agents, electron transfer agents and development accelerators are described, for example, in GB-A-2097140, GB-A-2131188, US-A-4859578 and US-A-4912025, which are incorporated herein by reference. It includes what is described.

The concentration of silver in the dispersion of silver particles may vary depending on the method of producing the silver particles from the carrier material and the silver halide particles. When silver particles are prepared from silver halide particles in gelatin, the silver to gelatin ratio is preferably at most 60 g, more preferably at most 40 g, even more preferably, for use as a conductive coating in coatings or to aid in the removal of the carrier medium. Is preferably 20 g or less.

Furthermore, depending on the intended use and the limitations of the apparatus used to handle the silver particles, the size, shape and size distribution of the silver particles can be controlled by the method of the present invention without imposing excessive restrictions, It is desirable to adjust various features of the shape of the silver particles as follows. It is preferred to have a large dimension of 10 μm or less, such as 0.1 to 10 μm, more preferably 0.25 to 5 μm. Although the particle shape can be controlled as discussed above, silver particles having a flat form can be, for example, planar [100] particles (approximately rectangular) or planar [111] particles (approximately hexagonal) or mixtures thereof. It is advantageous to provide. The plate-like [100] and [111] silver particles are silver particles prepared in a similar form manner from the plate-like [100] and [111] silver halide particles or silver having a similar shape to the plate-like [100] and [111] silver halide particles. Means particles. The flat silver particles preferably have an aspect ratio of at least 3: 1, more preferably at least 5: 1 and even more preferably from 10: 1 to 50: 1. The planar silver particles according to the present invention also preferably have a thickness of 0.5 μm or less, more preferably 0.2 μm or less, so that the particles overlap with each other when used in various applications.

A particular advantage of the present invention is the ability to control the size distribution of the silver particles produced, whether the produced silver particles are cubic, flat, or otherwise, without having to develop clumsy particle filters to screen particle sizes. to be. For example, to make the largest possible silver particles available as conductive ink (and thus provide maximum conductivity) via ink-jet printing, while minimizing the risk of clogging the ink-jet head due to larger particles In order to control the production of silver particles within certain parameters, it is advantageous. The most attractive method which can be achieved according to the present invention is to produce a narrow size distribution of silver halide particles and convert them into silver particles using conditions most favorable to physical phenomena or similar morphological conversion.

Preferably, in accordance with the invention, the coefficient of variation (COV) has a size distribution of 0.5 or less, more preferably 0.4 or less, even more preferably 0.25 or less, even more preferably 0.2 or less and most preferably 0.15 or less. Silver controls the dispersion of the particles. In an ideal situation, a COV of 0.1 is expected to be most desirable.

COV is a distribution attribute and can be calculated as the standard deviation divided by the mean (often quoted as a percentage). The COV of the size distribution in this case is based on their relative number according to the volume of the particles. In this regard, as low COV is achieved when the size and shape are uniform, COV is due to variations in volume as well as in the size of the particles.

The various possible preferred physical features of the silver particles may be appropriately individually or preferably in combination depending on the use in which the silver particles are used, but may be extended in the different embodiments discussed below.

In one embodiment of the invention, the conductive silver dispersion can be used as a coatable conductor for coating onto a substrate in a layered format for producing a conductive layered coating or in a patterned format for producing a patterned conductive coating. have. Uses of such conductive coatings include conductive back-plates for electronic devices such as printed circuit boards or electronic display devices, radio frequency (RF) or electromagnetic shielding films for devices such as mobile phones and laptop computers, and circuits or flexible printed circuits on printed circuit boards. do.

Dispersions of silver particles for preparing conductive coatings may include polymeric binder materials as carrier materials, and such suitable binder materials include the polymeric binders mentioned above as suitable carrier materials. Preferably, in order to produce a conductive layered coating or a conductive patterned coating, the dispersion comprises a curing agent, in particular when the coating is dried on a substrate and then cured when gelatin or similar polymeric binders are used. Such suitable curing agents are customary in photographic materials and are described in Research Disclosures, supra.

Alternatively, in order to provide a coating with excellent adhesion strength, mechanical resistance and solvent resistance upon drying, the carrier medium is preferably partially silylated (meth) acrylate as described in US-B2-6558746 in an aqueous medium. Copolymers or more preferably consist essentially of them. Typical silylated co-monomers include, for example, methacryloxypropyl trimethoxysilane and vinyl trimethoxy silane. Preferably, the copolymer has a degree of silylation of 0.05 to 50% and can be easily dispersed in water. Typical copolymers consist of, for example, 45% methylmethacrylate, 50% n-butylacrylate and 5% methacryloxypropyl trimethoxysilane.

Optionally, the silver dispersion used to prepare the conductive coating may be a silver flake powder, a copper flake powder, a metalized inorganic flake pigment and a powder of a conductive inorganic oxide (eg, fluoride-doped tin oxide or indium oxide / tin). Such as other conductive pigments.

Additional additives that may be optionally incorporated into the silver particle dispersion include wetting agents, antifoams, adhesion promoters, crosslinkers, and combinations thereof as desired.

Preferably, the silver particle dispersion according to this embodiment comprises 2.5 to 10% carrier material, 25 to 75% silver particles and optional conductive pigments, 13 to 72.5% water, 0 to 3% additional additives and 0 to 0.5 organic solvents. Has a composition comprising%.

The shape of the silver particles used according to this embodiment of the present invention (using a dispersion of silver particles as the conductive coating) can be of any shape such as flat, cube, filament, rod, and can be of any size and size distribution. Can be. However, planar silver particles are preferably used in both the layered conductive pattern and the patterned conductive coating. In the case of layered conductive coatings, it is believed that improved conductivity and the ability to provide thin layered materials are advantageous. Particularly in the case of patterned conductive coatings for use as conductive tracks, aligning the flat silver particles in accordance with the desired conductive track pattern allows them to have larger conductive silver particles and also to overlap these particles adjacent to other particles, resulting in relatively low Silver can provide improved conductivity by improving contact at the laydown, and thus conductivity.

Preferably, the aspect ratio of the plate-like silver particles preferred according to this embodiment is at least 3: 1, more preferably at least 5: 1 and most preferably from 10: 1 to 50: 1. The flat silver particles more preferably have a larger dimension of 0.1 to 10 μm, even more preferably 0.25 to 5 μm. Even more preferably, the flat silver particles have a thickness of 0.5 μm or less, and more preferably 0.05 μm or less.

In preparing the conductive layered coating, the silver dispersion can be applied to the substrate by any suitable method such as spraying, immersing the substrate in the bath of the dispersion, or roll-to-roll coating including bead coating, curtain coating.

In a preferred aspect of the present invention, conductive silver dispersions can be used, for example, as patterned conductive coatings that provide conductive tracks on a substrate. In order to produce a pattern of conductive silver dispersion, the dispersion can be coated onto the substrate in such a way that the pattern is produced. For example, by using the methods of our co-pending patent application described in International Patent Application No. PCT / GB2004 / 002591 and relating to a separate separate coating, it is possible to produce a patterned coating of conductive silver dispersion. have. According to this preferred feature of the present embodiment in which the silver dispersion can be coated in a patterned manner to produce conductive tracks, for example, the substrate to which the silver dispersion should be coated (preferably a flexible substrate) corresponds to the desired pattern. Treatment is performed to produce a surface pattern that defines the lyophilic (solvent affinity) and lyophilic (solvent repellent) zones so that when a coating of silver dispersion in the selected carrier medium is applied, the dispersion is lyophilic from the lyophilic zone. It will retract into the zone to create a patterned conductive track corresponding to the desired pattern.

In other embodiments, silver dispersions may be used as the conductive ink. The conductive ink can be, for example, an ink suitable for one or more of ink-jet, flexo, lithographic, gravure, concave and screen printing. Conductive inks are for example electronic components, conductive tracks on printed circuit boards, semiconductors, through interconnects, multilayer ceramic capacitors, conductive tapes, flexible electronics, RFID tag antennas, arrays of connections for display techniques, biological sensors and electrochemical sensors It may be suitable for any suitable conductive ink application, including the manufacture of electrodes, smart textiles, and the like.

For use in conductive track manufacture and most other conductive ink applications in electronics, it is desirable to use flat silver particles. Conductivity improved using planar silver particles is believed to result from superior and efficient interparticle connections because there are less interparticle connections, and planar silver particles tend to overlap to some extent.

Preferred ink compositions vary to some extent depending on the printing method and use.

For example, conductive inks for use in lithographic printing of electronic circuits preferably comprise flat silver particles which may have an average particle size of 1 to 10 μm, preferably 4 to 6 μm. Preferably, the aspect ratio of the flat silver particles is at least 3: 1, more preferably at least 5: 1 and most preferably from 10: 1 to 50: 1. The flat silver particles may have a thickness of 0.5 μm or less, even more preferably 0.05 μm or less. Optionally, such conductive inks may further comprise one or more types of smaller silver particles having the same or different shapes, such as cubes, to improve interparticle connectivity. Flat particles are particularly advantageous for lithography, where the high conductivity at low laydown of silver is attractive.

In the case of ink-jet printing, the size and shape of the silver particles used depend on the intended use and the like, but are limited by the dimensions of the ink-jet print head. In some applications, large, flat platelet particles may be advantageous, but it may be difficult to achieve laydown of such particles through an ink-jet method using small-bore ink-jet heads. Therefore, in the case of conductive inks in which the size of the particles is selected according to the size of the ink-jet head, for example, smaller plate-like particles (eg having larger dimensions of 1 μm or less), but preferably cube particles Is used for the conductive ink-jet ink, the size of which is selected according to the use and the size of the hole of the ink-jet head. By increasing the average size of the silver particles which can be used by precisely controlling the size distribution of the particles and thus increasing the conductivity without the risk of plugging the ink-jet head, the method of the present invention is applied to the ink-jet conductive ink. It can be used to advantage. As discussed above, the size distribution can be controlled by selecting parameters favorable to the physical phenomena of the silver halide particles and using well-established methods to control the size distribution in preparing dispersions of silver halide particles. Preferably, for this purpose, the coefficient of variation of the particle size of the silver particle dispersion according to the invention is 0.5 or less, more preferably 0.25 or less, even more preferably 0.2 or less.

Although the manufacturing costs of electronics in which conductive inks are generally used are quite high, it is expected that the cost of these devices can be reduced through improved manufacturing techniques and large scale manufacturing of flexible electronics. In this case, the cost of silver laydown, which is currently relatively insignificant, will become important, and the ability to provide improved conductivity with lower silver laydown through the method of the present invention will be a significant advantage. Furthermore, due to the improved conductivity at lower silver laydown, combined with control of size distribution, etc., more complex devices and circuits can be fabricated using conductive inks, such as ink-jet printing.

A conductive ink can be prepared by dispersing silver particles in a suitable ink-dispersant. A carrier in which a silver halide particle is converted to silver particles or a silver halide particle is converted to silver particles in a carrier medium suitable for use as an ink-dispersant using a carrier medium which forms a suitable ink-dispersant when co-dispersed with other materials. This can be achieved by replacing the medium with an ink-dispersant. Optionally, silver particles can be prepared from silver halide particles in a carrier medium that is also useful as an ink dispersant.

Suitable ink-dispersants vary depending on the application, but may include high-boiling solvents and binders as two or more separate components or as a single component. Other components for use in conductive inks include, for example, antioxidants, desiccants, adhesion-reducing agents, thickeners, curing agents, and surfactants.

The binder may be, for example, a carboxylic acid as described in WO-A-03 / 068874 for use in hydrocarbon resins, flexo printing or gravure printing containing alkyd resins (including styrenated alkyd resins) in lithography. Anhydride-functional aromatic vinyl polymers, such as those described in US-B-6332620 for use as thermosetting conductive inks, such as thermosetting resin systems comprising a mixture of epoxy resins, crosslinkers and catalysts.

The formulation of the conductive ink according to the present invention may be as typical in the field of conductive inks and belongs to the conventional ability of those skilled in the art.

In other embodiments, silver dispersions may be used as the conductive filler material. Silver dispersions are used as conductive filler materials in polymeric materials such as electronic enclosures, computer internal parts, mobile phones, portable devices, network routers, medical diagnostic and analytical equipment, aircraft and automotive equipment, conductive sheets, aircraft seals EMI, radio frequency (RF) shielding, conductivity and heat transfer to elastomers, sealants, adhesives, coatings, tapes and EMI gaskets for a wide range of applications, including conductive greases, conductive adhesives and epoxies, anisotropic connections and anisotropic adhesives Ability to provide

The silver particles of the present invention for use as conductive fillers may have any desired size, shape and size distribution that is controlled according to the conditions by the method. Depending on the use in which the conductive filler is used, the silver particles may be redispersed in other carrier materials. For example, silver particles may be dispersed in organosilicon compounds such as polyorganosiloxane or organohydrogensiloxane, examples of which can be found in US Pat. No. 2,679,777.

The substrate to which the silver particle containing conductive ink and / or conductive coating is applied depends on the intended use. The ink and coating may be applied to any suitable substrate that has been precoated or otherwise treated, and the substrate may be rigid or flexible but is preferably flexible. Suitable such substrates include rigid glass-reinforced epoxy laminates, metal pads and semiconductor components, adhesive coated polymer substrates, PCBs including polymer-based printed circuit boards (PCBs), ceramic substrates, polymer tapes (eg, multilayers). Dielectric green tape for ceramic devices), paper, glossy art paper, bond paper, semisynthetic paper (eg, polyester fibers), synthetic paper (eg, Polyart ™), resin coated paper, polymeric substrates, and composite materials do. Suitable polymers for use as the polymer substrate include polyethylene, polypropylene, polyesters, polyamides, polyimides, polysulfones and mixtures thereof. Substrates, particularly polymeric substrates, can be treated to improve the adhesion of the ink to the substrate surface. For example, the substrate may be coated with a polymer adhesive layer, or the surface may be chemically treated or corona treated.

When coating or printing onto a substrate in manufacturing a flexible electronic device or component, the support is preferably flexible to aid rapid roll-to-roll application. Optionally, in accordance with a preferred embodiment of the present invention, the support can be made by sucking a porous substrate (which may be paper), synthetic paper, resin coated paper or a porous polymer substrate, for example a coating composition or ink, into the support substrate. Inkjet paper is a porous substrate having the advantage of improving the contact between the silver particles to increase the conductivity.

The present invention is now described in more detail without restricting the invention with reference to the following examples and figures.

Example  One

3M AgNO ₃ and into a reaction vessel containing 240 g of conventional bone gelatin, 1.5 ml of PLURONIC® 31R1 (oxylane, methyl-, polymer) and maintained at 75 ° C. made of 6.9 liters of demineralized water. An emulsion (dispersion) of 100% AgCl cube particles was prepared by double-jet precipitation of NaCl solution under controlled flow and pAg conditions. This solution was adjusted to pAg 6.8 with KCl. The initial AgNO ₃ solution flow was 32 ml / min for 2.5 minutes, then spiked to 200 ml / min over 25 minutes. The flow was maintained at 200 ml / min until 4 liters of AgNO ₃ solution was consumed. The resulting particles had a narrow size width (coefficient of variation 0.22) and an edge length of 0.54 μm as measured by electrolytic grain analysis.

The resulting emulsion / dispersion was UF washed to remove unwanted reaction byproducts up to solution conductivity <10mS, pAg 6.8 and pH 5.6 (UF = ultrafiltration through membrane). After the washing step an additional 20 g of gelatin per molar equivalent of silver was added.

Diluted samples of the dispersion were used to obtain SEM (scanning transcription micrographs) images of the cube silver chloride particle dispersion, which is shown in FIG. 1.

A developer composition (1 liter) was prepared as follows:

50.0 g of sodium erythrate (developer),

3.0 g of HMMP (developer),

8.0 g of sodium thiosulfate (fixing agent),

20 g of K ₂ CO ₃ (buffer).

900 ml of demineralized water were added and pH was adjusted to 11.5 with BAS-2013.

Fill up to 1000 ml with demineralized water.

To fogging the silver chloride particles, a portion of the silver chloride emulsion / dispersion (including 2 moles of silver chloride) in the gelatin maintained at 40 ° C. was treated with sodium hydroxide to adjust the pH of the emulsion to 12. The fogging emulsion was also added immediately to a vessel containing 15 liters of developer composition maintained at 40 ° C. (quickly over about 2 seconds in red light) and stirred at high speed using a post-stirrer. The contents of the container turned gray in 2-3 seconds. The pH was kept above 10 by careful addition of sodium hydroxide solution during the early stages of development of the silver chloride particles (approximately 3 minutes), and then the pH was adjusted back to 11 for an additional 10 minutes. The resulting silver particles were UF washed and concentrated by ultrafiltration to a solution conductivity of <20 mS. The silver concentration of the resulting silver dispersion was determined to be 0.80 Ag mol / kg by ICP (inductively coupled plasma spectroscopy).

SEM images of the diluted samples of the resulting silver dispersion were obtained, which is shown in FIG. 2. As a result of the qualitative comparison of FIGS. 1 and 2, it is evident that the silver particles were produced by a similar form (developing) process (ie, they retained most of the shape of the silver chloride particles from which they were produced).

Example  2

The double jet method by pumping into a reaction vessel containing 195 g of oxidized gelatin and 4373 g of demineralized water, maintained at pAG of 35 ° C. and 7.6 for 1.6 minutes, at 78 ml / min under controlled pAg conditions starting with 1 M AgNO ₃ and NaCl solution. The precipitate (dispersion) of 100% AgCl plate [100] particles was precipitated using At this point, a solution made at 9.285 liters at 35 ° C., containing 2.25 g NaCl and 0.57 g KI, was added to the reaction vessel and held for 5 minutes. At this point, growth was continued using 4M AgNO ₃ and NaCl solution added at 15 ml / min under controlled pAg conditions. The temperature was increased linearly from 35 ° C. to 70 ° C. over 40 minutes. The flow was then stopped for 15 minutes and resumed for an additional 45 minutes, during which the flow rate increased linearly from 15 ml / min to 42.3 ml / min, at which time 8 moles were consumed. The emulsion was left at 70 ° C. for another 30 minutes, then cooled to 40 ° C. and washed.

The resulting emulsion / dispersion was UF washed to remove unwanted reaction byproducts up to solution conductivity <10mS, pAg 6.8 and pH 5.6. After the washing step an additional 20 g of gelatin per molar equivalent of silver was added.

The resulting [100] platen silver halide particles are clearly seen in the SEM images obtained and shown in FIG. 3.

The developer composition was prepared as follows:

50.0 g of sodium erythrate (developer),

3.0 g of HMMP (developer),

8.0 g of sodium thiosulfate (fixing agent),

20 g of K ₂ CO ₃ (buffer).

Add 900 g of demineralized water and adjust the pH to 11.5 with BAS-2013.

Fill up to 1000 ml with demineralized water.

To fogging the silver chloride particles, a portion of the silver chloride emulsion / dispersion (including 2 moles of silver chloride) in the gelatin maintained at 40 ° C. was treated with sodium hydroxide to adjust the emulsion to pH 12. The fogging emulsion was also added immediately to a vessel containing 15 liters of developer composition maintained at 40 ° C. (quickly over about 2 seconds in red light) and stirred at high speed using a post-stirrer. The contents of the container turned gray in 2-3 seconds. The pH was lowered to 9.7 over the first three minutes and then adjusted back to 11 for an additional 10 minutes. The resulting silver particles were UF washed by ultrafiltration and concentrated to a solution conductivity of <20 mS. The silver concentration of the resulting silver dispersion was determined to be 0.83 Ag mol / kg by ICP (inductively coupled plasma spectroscopy).

4 shows an SEM image of the resulting silver particles that are apparently flat plate [100] particles. Again, by comparing the silver chloride particles shown in FIG. 3, it is clear that the silver particles retain most of the shape of the silver chloride particles from which they are produced. By comparing the silver particles produced in Example 2 (FIG. 4) with the silver particles produced in Example 1 (FIG. 2), the size and shape of the silver particles are adjusted by adjusting the size and shape of the silver chloride particles from which the silver particles are produced. It is obvious that it can be adjusted accurately. In addition, a wide variety of size and shape features can be achieved with adjustable. In Example 1, cubic silver particles (FIG. 2) were produced having an edge length of 0.5 to 1 μm (qualitative) (0.54 μm when measured), whereas in Example 2 3 to 4 μm (qualitative) [100] plated silver particles having a longer edge length of (4) are produced.

Example  3

An emulsion (dispersion) of 100% AgCl plate [111] particles was precipitated in the presence of adenine using the method described in Example 1 of US-A-5176991 [CG Jones et al.] Except the coagulation washing step. .

The resulting emulsion / dispersion was UF washed to remove unwanted reaction byproducts up to a solution conductivity of <10mS, pAg of 6.8 and pH of 5.6.

The SEM image (FIG. 5) shows a sample of the approximately hexagonal [111] plate silver chloride particles obtained.

The developer composition was prepared as follows:

50.0 g of sodium erythrate (developer),

3.0 g of HMMP (developer),

4.0 g of sodium thiosulfate (fixing agent),

20 g of K ₂ CO ₃ (buffer).

Add 900 g of demineralized water and adjust the pH to 11.5 with BAS-2013.

Fill up to 1000 ml with demineralized water.

To fogging the silver chloride particles, a portion of the silver chloride emulsion / dispersion (including 0.07 mol of silver chloride) in the gelatin maintained at 40 ° C. was treated with sodium hydroxide to adjust the pH of the emulsion to 12 and maintained at pH 12 for 10 minutes. To maintain high pH during development, a composition comprising 240 ml of developer composition and 70 ml of 100 g / l sodium hydroxide solution, maintained at 40 ° C., was added to the silver chloride emulsion. After 5 minutes the pH was lowered to 5.3 and 0.2 ml of Sulfonyl ™ CT131 surfactant was added to help disperse the resulting silver particles. The dispersion was allowed to stand for 24 hours and followed 90% of the supernatant.

FIG. 6 shows an SEM image of the resulting [111] plated silver particles reduced in analogy form from silver chloride particles by the method of the present invention as can be seen by comparison with FIG. 5.

Example  4

An emulsion (dispersion) of 100% silver chloride flat plate [100] particles was prepared according to the method described in Example 2 above.

The developer composition was prepared as follows:

50.0 g of sodium erythrate (developer),

3.0 g of HMMP (developer),

4.0 g of sodium thiosulfate (fixing agent),

20 g of K ₂ CO ₃ (buffer).

Add 900 g of demineralized water and adjust the pH to 11.5 with BAS-2013.

Fill up to 1000 ml with demineralized water.

To fogging the silver chloride particles, a portion of the silver chloride emulsion / dispersion (containing 0.1 mol of silver chloride) in gelatin maintained at 40 ° C. was treated with 0.2 ml of a SnCl ₂ solution (10 g / l) in 0.6 M HCl and held for 10 minutes. 240 ml of developer solution and 70 ml of 100 g / l sodium hydroxide solution to maintain high pH during development were added to the emulsion at 40 ° C. After 5 minutes the pH was lowered to 5.3 and 0.2 ml of Sulfonyl ™ CT131 surfactant was added to help disperse the resulting silver particles. The silver dispersion was then centrifuged several times to wash and concentrate the dispersion.

FIG. 7 shows SEM images of the resulting silver particles which can be clearly recognized as [100] planar particles, which again retained most of the shape of the silver chloride particles from which they were produced (see FIG. 3).

Example  5

Using an RK automated bar coater using a coating bar of 24 to 40 μm, samples of silver dispersions (each dispersion 1 to 4, respectively) prepared according to Examples 1 to 4 were used as Estar® polyethylene based, ink- Coating on various supports such as jet media and other paper types. Porous ink-jet media had more coated silver laydown (measured using XRF) due to the substrate absorbing liquid as the coating bar traversed the sample.

The resistivity across the 31 mm disc was measured for each coated sample (four replicate measurements across different axes and averaged). The silver laydown and resistivity (Ω / square) of each sample are listed in Table 1.

This demonstrates that various silver dispersions can be used to produce conductive coatings on a wide range of supports. Preferably, larger silver laydowns may appear to provide good conductivity (see coatings B and C). Comparing coatings C and E, it can be clearly seen that larger and flatter [100] planar silver particles provide better conductivity on porous supports than cubic silver particles in similar laydown.

Example 6 -Flexo Printing

A 60 g sample of the silver dispersion prepared in Example 2 was further concentrated by centrifugation at 3,000 RPM for 10 minutes at 40 ° C. for rotary settling. 45 g of the supernatant was removed, leaving a material at the level of 3.33 Ag mol / kg. The samples were redispersed by stirring by hand and using Sony-probe for 5 minutes, then printed onto various substrates using RK flexo proofer with anilox roller at 2001pi. Both patterned and unpatterned rollers were used. The results of the patterned rollers showed that the material could be flexographically printed. The results of the unpatterned rollers provided the XRF and resistivity measurements (across the 31 mm disc) as detailed in Table 2 below. As with some commercially available conductive flexo inks, more than one layer of ink laydown was required to produce satisfactory conductivity, and the table shows the conductivity of two and three chains in overlapped state.

Example 7 Ink-Jet Printing

A silver dispersion prepared according to the method of Example 1 was prepared with ethanesulfonic acid, 2- (2- (2- (4- (1,1,3,3-tetramethylbutyl) phenoxy) ethoxy) ethoxy) Treated with 2% by volume of surfactant solution containing 71.8 g / kg sodium salt and mixed at 30 ° C. immediately before printing. The dispersion was jetted onto various substrates using a valve-jet device such as described in US-A-2004 / 0110101. This method was used to print the lines and black areas of the dots. For a wide range of nozzle diameters on each substrate, the silver laydown and conductivity (resistance across a 31 mm disk) of black-printed silver was measured. The results are shown in Table 3.

The results show that the conductive layer of silver can be produced by ink-jet printing of the silver dispersion prepared according to the invention.

Claims (42)

A method of making a conductive ink, conductive filler and / or conductive coating comprising silver particles to impart conductivity, alone or in combination with other conductive materials, Providing a dispersion of silver halide particles in a carrier medium; Treating the dispersion of silver halide particles to convert the silver halide particles into silver particles, thereby producing a dispersion of silver particles in a carrier medium; And Further processing the dispersion of silver particles in the carrier medium to produce a conductive ink, a conductive filler and / or a conductive coating. The method of claim 1, And said silver halide particles comprise silver chloride. The method of claim 2, Wherein said silver halide particles comprise silver chloride in an amount of at least 90%. The method of claim 3, wherein And wherein said silver halide particles comprise silver chloride at least 99.5%. The method according to any one of claims 1 to 4, Wherein said dispersion of silver particles comprises silver particles having dimensions in one direction of 0.03 to 10 μm. The method of claim 5, Wherein said dispersion of silver particles comprises silver particles having dimensions in one direction of 0.25 to 5 μm. The method according to any one of claims 1 to 6, Wherein said silver halide particles are tabular grains. The method of claim 7, wherein Wherein said silver particles are planar particles having a form substantially corresponding to that of a silver halide planar grain. The method according to claim 7 or 8, Wherein said platelet grain has an aspect ratio of at least 3: 1. The method of claim 9, And said planar grains have an aspect ratio of at least 5: 1. The method of claim 10, Said planar grains having an aspect ratio of 10: 1 to 50: 1. The method according to any one of claims 1 to 11, Treating the dispersion of silver halide particles comprises fogging the silver halide particles and reducing the fogged silver halide particles with a developer composition. The method of claim 12, The fogging of the silver halide particles by treatment with a reducing agent, exposure of the silver halide particles to radiation where they are sensitive, pH adjustment of the silver halide dispersion and / or incorporation of a source of silver ions or silver ions into the dispersion of the silver halide particles Way. The method according to any one of claims 1 to 13, The carrier medium is gelatin. The method of claim 14, And replacing the carrier medium of the dispersion of silver particles with a second carrier medium different from the carrier medium. The method of claim 15, Wherein said second carrier medium is suitable for use as an ink-dispersant. The method according to any one of claims 1 to 16, The method is a method of producing a conductive ink. The method of claim 17, Wherein said conductive ink is suitable for at least one of ink-jet, flexo, lithographic, relief, gravure, and screen printing. The method of claim 18, The conductive ink is suitable for ink-jet printing, The further processing step comprises compounding a dispersion of silver particles for use in ink-jet printing, Wherein said dispersion of silver particles comprises silver particles having a largest dimension of 1 μm or less and a cubic or flat form, and having a size distribution of a coefficient of variation of 0.5 or less. The method of claim 17, The conductive ink is suitable for lithography, Said further processing step comprises blending a dispersion of silver particles for use in lithography, And wherein said dispersion of silver particles comprises silver particles having a planar form with a maximum dimension of 10 μm or less and an aspect ratio of 5: 1 or more. The method according to any one of claims 1 to 17, The method is a method of preparing a conductive filler, Further processing of the dispersion of silver particles comprises mixing the dispersion of silver particles with a composition that produces a component in which the silver dispersion is used as a conductive filler. The method according to any one of claims 1 to 17, The method is a method of producing a conductive coating, Wherein the further processing of the dispersion of silver particles comprises coating the dispersion of silver particles onto the support with a laydown of silver particles sufficient to provide a conductive coating. The method of claim 22, The conductive coating is a patterned conductive coating defining a conductive track, The method treats the support substrate to produce a lyophilic zone and a lyotropic zone defining a desired pattern of conductive tracks and then coating the dispersion of silver particles onto the support according to the desired pattern. How to produce. A conductive ink, conductive filler or conductive coating obtainable by the method according to any one of claims 1 to 23. A conductive ink for ink-jet printing, comprising a dispersion of silver particles having silver particles in the form of a cube or plate, wherein the dispersion has a size distribution with a coefficient of variation of 0.5 or less. A conductive ink for lithography comprising a dispersion of silver particles having silver particles having a flat shape with a maximum dimension of 10 μm or less and an aspect ratio of 5: 1 or more. A conductive filler comprising a dispersion of silver particles having a planar form with a maximum dimension of 10 μm or less and an aspect ratio of at least 5: 1. A conductive coating comprising a dispersion of silver particles having a planar form with a maximum dimension of 10 μm or less and an aspect ratio of at least 5: 1. A process for preparing silver dispersions for use as or in the manufacture of conductive inks, conductive fillers and / or conductive coatings, Providing a dispersion of silver halide particles in a carrier medium; And Treating the dispersion of silver halide particles to convert the silver halide particles into silver particles, thereby producing a dispersion of silver particles in a carrier medium, A) Coated conductivity expressed as resistivity of 1000 Ω / square or less; B) at least 50% of plate-like silver particles having an aspect ratio of at least 3: 1; And C) A dispersion characterized by silver particles having at least one of the size distributions of the particles having a coefficient of variation of 0.4 or less. The method of claim 29, 17. A method further characterized by any one of the features defined in any of claims 7-11, 15 and 16. The method of claim 29 or 30, 15. A method further characterized by any one of the features defined in any of claims 2-6 and 12-14. As a conductive ink, conductive filler and / or conductive coating or as a dispersion of silver particles for use in the preparation thereof, The silver particles dispersed in a carrier medium at a concentration such that the dispersion of silver particles can impart a conductivity represented by a resistivity of 1000 Ω / square or less to the ink, filler, and / or coating prepared therefrom, wherein the silver particles are flat Having a phase form and an aspect ratio of at least 3: 1, and / or wherein the silver dispersion has a size distribution of silver particles having a coefficient of variation of 0.5 or less, Dispersion of silver particles. 33. A method of manufacturing an electronic circuit, comprising applying a dispersion of silver particles according to claim 32 to a substrate in a desired pattern of conductive tracks. The method of claim 33, wherein 27. A method comprising applying a conductive ink according to any of claims 24 to 26 to a substrate. The method of claim 33, wherein A method comprising applying a conductive ink according to claim 24 or 25 to a substrate via ink-jet printing. The method of claim 33, wherein 27. A method comprising applying the conductive ink according to claim 26 to a substrate via lithography. The method of claim 33, wherein The substrate is processed to create a lyophilic zone and a lyotropic zone defining a desired pattern of conductive tracks to be produced, and coating the patterned substrate with a silver dispersion, thereby producing a desired track of conductive tracks of silver particles. Producing according to the method. The method of claim 37, wherein Coating said silver dispersion through a continuous separate coating. In producing a conductive ink, conductive filler and / or conductive coating by treating the dispersion of silver halide particles to convert the silver halide particles into silver particles to produce a dispersion of silver particles from which a conductive ink, conductive filler or conductive coating is produced. Of silver halide particles. Silver halide in preparing a dispersion of silver halide particles for controlling the individual size, size distribution and / or shape of the silver particles in the silver particle dispersion by treating the dispersion of silver halide particles so that the dispersion of silver halide particles is converted into a dispersion of silver particles. Use of factors to control particle size, size distribution and / or morphology. The method of claim 40, Use of the dispersion of silver halide particles to cause the dispersion of silver halide particles to be converted into a dispersion of silver particles under conditions favoring physical phenomena rather than chemical phenomena. Use of a factor to control the individual physical and chemical developability of the fogging silver halide to control the shape of the silver particles produced by treating the silver halide particles such that the silver halide particles undergo a fogging step and a developing step.

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